1. Field of the Invention
The invention relates to a mobile terminal, and more particularly to a method of charging a battery mounted in a mobile terminal
2. Description of the Related Art
A mobile terminal such as a mobile phone, PHS (Personal Handy-phone System), PDA (Personal Data Assistance or Personal Digital Assistant) and a note-type personal computer has been designed to include a battery in a case thereof for supplying electric power to electronic parts constituting a mobile terminal. A battery is designed to be able to be electrically connected to an external AC power source, and to be charged when electrically connected to the AC power source.
A system for charging a battery is suggested, for instance, in Japanese Patent Application Publications Nos. 2002-58174 and 2001-136675 (patent references 1 and 2).
In the system suggested in patent reference 1, a temperature around a capacitor is detected, and a voltage of a battery observed when fully charged is varied in accordance with the detected temperature. When a voltage of a battery is over the voltage of a battery observed when the battery is fully charged, the battery is stopped from being charged.
In the system suggested in patent reference 2, a temperature of a battery is detected. A target temperature to which a temperature of a battery is aimed to reach is varied in accordance with the detected temperature, and a current for charging a battery is varied in accordance with the target temperature. If a temperature of a battery exceeds a target temperature, a battery is stopped from being charged.    Patent reference 1: Japanese Patent Application Publication No. 2002-58174    Patent reference 2: Japanese Patent Application Publication No. 2001-136675
In a mobile terminal, a charging circuit produces calorific power when it charges a battery, and some electronic parts such as CPU and a signal transmitter/receiver also produce calorific power.
In the systems suggested in the above-mentioned patent references 1 and 2, since a current for charging a battery is varied in accordance with a temperature of a battery, if the systems suggested in the above-mentioned patent references 1 and 2 were applied to a mobile terminal, it would not be possible to control a temperature of a mobile terminal, taking into consideration calorific power produced by electronic parts other than a charging circuit.
Hence, if electronic parts other than a charging circuit, and a battery simultaneously produce calorific power, a temperature of a mobile terminal excessively rises, resulting in that a surface temperature of a case also rises, and a user of a mobile terminal feels ill when he/she makes direct touch with a surface of a case. In order to solve this problem, if a target voltage of a battery and a target temperature of a battery are set low, a current for charging a battery is reduced even when electronic parts other than a charging circuit do not produce calorific power, resulting in another problem that it takes too much time to charge a battery.